The present invention relates to an engine to be mounted on a vehicle, such as straddle-type four-wheeled all terrain vehicles or two-wheeled motorcycle, more specifically a vehicle engine having an reverse gear train.
FIG. 10 shows a transmission of a conventional engine of a vehicle for driving on rough terrain, which has the reverse gear train. A reverse idle gear shaft 202 disposed in a transmission chamber 201 is extended along a full left-to-right length of a crank case 203 and is rotatably supported on the left and the right side walls 204a, 204b of the transmission chamber 201 by means of bearings 205. A smaller-diameter reverse idle gear 210 is disposed on the left end of the reverse idle gear shaft 202, and a larger-diameter reverse idle gear 211 is disposed on the right end. The larger-diameter reverse idle gear 211 engages a low gear 215 of a transmission input shaft 212, and the smaller-diameter idle gear 210 engages the reverse gear 216 of a transmission output shaft 213.
In the structure shown in FIG. 10, the reverse idle gear shaft 202 is supported on the left and the right ends of the transmission chamber 201, extended fully therebetween. Two reverse idle gears 210, 211 are mounted on the left and the right ends of the reverse idle gear shaft 202. The low gear 215 on the transmission input shaft 212 is longitudinally elongated to engage the larger-diameter reverse idle gear 211. This structure makes the reverse idle gear shaft 202 unnecessarily long and adds weight. Furthermore, even in disposing the reverse idle gears 210, 211 near the left and the right bearings 205, 205 to prevent the generation of vibrations due to bending, the excessive length of the reverse idle gear shaft 202 itself is a cause of gear noise.
On the other hand, in reducing the shaft length of the reverse idle gear shaft 202, the reverse idle gears 210, 211 are disposed at an intermediate location between the left and the right crank case members 204a, 204b, which restricts the transmission gear trains on the respective transmission shafts 212, 213 and hinders efforts to make the transmission gear arrangement more compact.
In contrast to the structure having two reverse idle gears as described above, the transmission as described in, e.g., the specification of Japanese Utility Model Publication No. 3872/1989, has one reverse idle gear, and the reverse idle gear is rotatably mounted on a shift cam shaft supported on the left and the right end walls of the crank case.
However, one reverse idle gear restricts the reduction gear ratio more than two reverse idle gears and makes it difficult to allow for a large reduction gear ratio. When a large reduction gear ratio is forced, the diameter of the reverse idle gear becomes too large, which makes the transmission uselessly large. Terrain
In view of the above-described problem the present invention has been made. An object of the present invention is to provide a vehicle engine comprising a transmission having one reverse idle gear, in which a configuration of the engine, an arrangement of the reverse idle gear and a structure for supporting the reverse idle gear shaft are contrived to thereby compact and lighten the transmission and the engine.
The present invention relates to a vehicle engine comprising a crank case including a crank chamber and a transmission chamber; a crank shaft disposed in the crank chamber; and a transmission gear mechanism disposed in the transmission chamber, including an reverse idle gear shaft and one reverse idle gear mounted on the idle gear shaft; and cover chambers housing a generator and a clutch being disposed respectively on both sides of the crank chamber in the direction of the crank shaft, the reverse idle gear having a part projected from the transmission chamber to one of the cover chambers.
According to the present invention, the interior space of the cover chamber can be utilized as a part of the space where the reverse idle gear is dipsoed, whereby even when the reverse idle gear has a larger diameter, the transmission chamber and the engine can be kept compact.
It is preferable that the transmission chamber is projected beyond the crank chamber toward one end of the crank shaft, and the reverse idle gear being disposed in the projected portion of the transmission chamber, and a gear insertion hole is formed in a partition wall between the transmission chamber and the cover chamber, and the part of the reverse idle gear is projected to the cover chamber through the gear insertion hole.
In this structure, the bulged part of the transmission chamber in the direction of the crank shaft is utilized to dispose the reverse idle gear, and a part of the reverse idle gear is projected toward the cover chamber neighboring the bulged part, whereby the configuration of the cover chamber and the transmission chamber, and their mutual positional relationship are utilized to arrange the reverse idle gear without uselessly increasing the space. Furthermore, the partition wall between the cover chamber and the transmission chamber can be effectively utilized. The engine can be made more compact.
It is preferable that a shaft support member is secured to an end wall of the transmission chamber on the side of one end of the crank shaft, and the reverse idle gear shaft with the reverse idle gear mounted thereon has both ends supported by the end wall of the transmission chamber and the shaft support member.
In this structure, the reverse idle gear and the reverse idle gear shaft can be easily mounted on the crank case, and the reverse idle gear shaft can decrease the length, so that the weight and the space for arranging the shaft are decreased. The reverse gear shaft is shortened and has both ends supported, whereby the bending moments of the shaft generated in the operation can be small, which can decrease-gear noises.
It is preferable that the transmission gear mechanism further includes a shift rod, and the shift rod is supported by the shaft support member supporting the reverse idle gear shaft.
In this structure, the reverse gear shaft and the shift rod are supported by one shaft support member, whereby a part number of the transmission can be decreased, and accordingly the weight can be decreased.
The present invention relates to a vehicle engine comprises a crank case including a crank chamber and a transmission chamber; a crank shaft having a center axis disposed in the crank chamber; a transmission gear mechanism disposed in the transmission chamber and including a transmission output shaft having a center axis, a transmission input shaft having a center axis, a reverse idle gear shaft having a center axis with a reverse idle gear mounted thereon, and a change drum shaft having a center axis, cover chambers housing a generator and a clutch being disposed respectively on both sides of the crank chamber in the direction of the crank shaft, the transmission input shaft being arranged one side of a straight line interconnecting the center axis of the crank shaft and the center axis of the transmission output shaft, and the change drum shaft being arranged on the other side of the straight line interconnecting the center axis of the crank shaft and the center axis of the transmission output shaft, and the reverse idle gear shaft is disposed in a region surrounded by the center axis of the crank shaft, the center axis of the transmission output shaft, the center axis of the transmission input shaft and the center axis of the change drum shaft.
According to the present invention, the space surrounded by the above-described four shafts is effectively utilized to position the reverse idle gear shaft, whereby the transmission can be compact.
It is preferable that the reverse idle gear shaft and the change drum shaft are arranged below a straight line interconnecting the transmission input shaft and the transmission output shaft.
In this structure, the space of an upper part in the transmission chamber can be used as a space for arranging a starting mechanism of the engine, such as a starting motor, etc.
It is preferable that the transmission gear mechanism includes a shift rod, and the reverse idle gear is arranged, partially overlapping the shift rod and the change drum as viewed in the direction of extension of the crank shaft.
In this structure, the reverse idle gear is positioned, overlapping the shift rod and the change drum as viewed in the direction of the shaft, whereby the transmission and engine having an reverse gear train can have smaller vertical and horizontal dimensions as viewed in the direction of the shaft and therefore the engine can have smaller weights.
It is preferable that a shaft support member is secured to an end wall of the transmission chamber on the side of one end of the crank shaft, the reverse idle gear shaft with an reverse idle gear mounted thereon has both ends supported by the end wall of the transmission chamber and the shaft support member, and the shift rod is supported by the shaft support member.
In this structure, the reverse idle gear and the reverse idle gear shaft can be easily mounted. The reverse idle gear shaft is shortened to thereby decrease the weight and the space for arranging the shaft. The reverse idle gear shaft is shortened and has both ends supported, whereby bending moments of the reverse idle gear shaft in the operation can be small, which prevents the generation of the gear noises.
It is preferable that the reverse idle gear of the reverse idle gear shaft has a part projected out of the transmission chamber into the cover chamber housing the generator.
In this structure, the cover chamber housing the generator is used as a part of the space for arranging the reverse idle gear, whereby an empty space for arranging the reverse idle gear can be easily ensured.
It is preferable that the transmission input shaft and the transmission output shaft have respective shift sleeves for shifting the gears, and all of the shift forks which are engaged with the shift sleeves of the transmission input shaft and the transmission output shaft, are mounted on said shift rod.
In this structure, a number of the shift rods can be minimized, which also can make the transmission compact and light.
The above and further objects and features of the present invention will be more fully apparent from the following detailed description with accompanying drawings.